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PDBsum entry 1xz6
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References listed in PDB file
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Key reference
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Title
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Structural basis for the inactivity of human blood group o2 glycosyltransferase.
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Authors
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H.J.Lee,
C.H.Barry,
S.N.Borisova,
N.O.Seto,
R.B.Zheng,
A.Blancher,
S.V.Evans,
M.M.Palcic.
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Ref.
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J Biol Chem, 2005,
280,
525-529.
[DOI no: ]
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PubMed id
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Abstract
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The human ABO(H) blood group antigens are carbohydrate structures generated by
glycosyltransferase enzymes. Glycosyltransferase A (GTA) uses UDP-GalNAc as a
donor to transfer a monosaccharide residue to Fuc alpha1-2Gal beta-R
(H)-terminating acceptors. Similarly, glycosyltransferase B (GTB) catalyzes the
transfer of a monosaccharide residue from UDP-Gal to the same acceptors. These
are highly homologous enzymes differing in only four of 354 amino acids,
Arg/Gly-176, Gly/Ser-235, Leu/Met-266, and Gly/Ala-268. Blood group O usually
stems from the expression of truncated inactive forms of GTA or GTB. Recently,
an O(2) enzyme was discovered that was a full-length form of GTA with three
mutations, P74S, R176G, and G268R. We showed previously that the R176G mutation
increased catalytic activity with minor effects on substrate binding. Enzyme
kinetics and high resolution structural studies of mutant enzymes based on the
O(2) blood group transferase reveal that whereas the P74S mutation in the stem
region of the protein does not appear to play a role in enzyme inactivation, the
G268R mutation completely blocks the donor GalNAc-binding site leaving the
acceptor binding site unaffected.
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Figure 1.
FIG. 1. Active site of the O2 glycosyltransferase triple
mutant showing the observed electron density in the active site
of the unliganded enzyme with ordered Arg-268 side chain (a),
and the enzyme crystallized in the presence of the native H
antigen acceptor that causes the Arg-268 and Leu-266 side chains
to become disordered (b).
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Figure 2.
FIG. 2. Overlap of the unliganded O2 enzyme showing Arg-268
and adjacent residues with the observed position of acceptor
(green) and UDP (magenta) of wild-type GTA. The position of the
GalNAc residue (magenta) has been modeled after Patenaude et al.
(6) and shows severe conflicts with the Arg-268 side chain that
completely blocks the sugar residue from the active site.
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2005,
280,
525-529)
copyright 2005.
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